a. Field of the Invention
This invention relates to a system for diagnosis and treatment of tissues in a body. In particular, the instant invention relates to a system for optimizing the degree of mechanical and/or electrical coupling between an ablation catheter and tissue and for evaluating lesions in the tissue created by the ablation catheter.
b. Background Art
It is well known to use ablation catheters to create tissue necrosis in cardiac tissue to correct cardiac arrhythmias (including, but not limited to, atrial fibrillation, atrial flutter, atrial tachycardia and ventricular tachycardia). Arrhythmia can create a variety of dangerous conditions including irregular heart rates, loss of synchronous atrioventricular contractions and stasis of blood flow which can lead to a variety of ailments and even death. It is believed that the primary cause of many arrhythmias is stray electrical signals within one or more heart chambers. The ablation catheter imparts ablative energy (e.g., radiofrequency energy, light energy, ultrasound, or thermal (cryo or heat based) energy) to the heart tissue to create a lesion in the heart tissue. This lesion disrupts undesirable electrical pathways and thereby limits or prevents stray electrical signals that lead to arrhythmias.
Approximately 100 Joules of energy may be adequate to create a lesion in atrial tissue that is sufficient to disrupt an electrical pathway through the tissue. Because clinicians often lack sufficient real-time information regarding the degree of coupling between the ablation catheter and tissue and regarding the lesion being created, however, clinicians regularly apply significantly greater amounts of energy to insure an effective lesion. For example, it is common for clinicians to use a power setting of fifty (50) Watts for sixty (60) seconds thereby applying 3000 Joules of energy to the tissue. The excessive energy application increases several risks associated with ablation therapy including perforation of tissue, coagulation of the blood which can result in creation of a thrombus, and tissue or steam pops resulting from the application of heat to water inside the tissue which may cause the water to boil and burst through the tissue wall.
The inventors herein have recognized a need for a system and method for diagnosis or treatment of tissue within a body that will minimize and/or eliminate one or more of the above-identified deficiencies.